The present invention relates to a hydrogenated polymer (may also be referred to as xe2x80x9ca hydrogenated product of an aromatic vinyl polymerxe2x80x9d) obtained by hydrogenating an aromatic vinyl polymer, a resin composition comprising the hydrogenated polymer and a production process of a substrate for information recording media, and more particularly to a substrate for information recording media, which is excellent in mechanical strength, a resin composition excellent in moisture resistance and molding and processing ability, and a hydrogenated product of an aromatic vinyl polymer suitable for use in providing such substrate and resin composition. The present invention also relates to a high-quality hydrogenated product of an aromatic vinyl polymer containing little foreign matter.
Hydrogenated polymers obtained by hydrogenating aromatic rings in aromatic vinyl polymers such as polystyrene have heretofore been known to be molding materials suitable for use in substrates for information recording media, which are small in birefringence. For example, Japanese Patent Application Laid-Open No. 43910/1988 proposes the use of polymers containing at least 30% by weight of a vinylcyclohexane polymer component in its molecular chain for molding materials for optical disk substrates. The publication specifically discloses examples where a hydrogenated product of an aromatic vinyl polymer having a hydrogenation rate of 97% at the aromatic ring portion thereof, a weight average. molecular weight (Mw) of 92,000 and a molecular weight distribution (Mw/Mn) of 1.84, or a hydrogenated product of an aromatic vinyl polymer having a hydrogenation rate of 85% at the aromatic ring portion thereof, a weight average molecular weight (Mw) of 150,000 and a molecular weight distribution (Mw/Mn) of 1.87 was used to mold an optical disk substrate.
However, these optical disk substrates are recognized to be high in light transmittance, small in water absorptivity and relatively small in birefringence, but they have such problems that their mechanical strength is insufficient, the value of birefringence does not reach a sufficiently satisfactory level, and reliability such as long-term heat resistance is insufficient.
Japanese Patent Application Laid-Open No. 318015/1989 proposes optical disk substrates formed of a polyvinylcyclohexane resin having a number average molecular weight (Mn) of at least 50,000 and a softening point of at least 150xc2x0 C. The publication specifically discloses an example where polyvinylcyclohexane having a hydrogenation rate of 99% at the aromatic ring portion thereof and a weight average molecular weight (Mw) of at least 160,000 was used to mold an optical disk substrate. However, the birefringence of this optical disk was not reduced to a satisfactory level.
For reasons of the above-described facts, there is a strong demand for development of a molding material for providing a substrate which has a sufficiently small birefringence value, is excellent in mechanical strength and is balanced among various properties required of the substrate at a high level.
Further, it has been proven that in the hydrogenated products of the aromatic vinyl polymers, impurities such as finely particulate matter and fibrous matter are mixed in various processes such as their polymerization processes, hydrogenation processes and post-treatment processes, polymerization catalysts and hydrogenation catalysts remain, or gel-like matter is formed, and so they contain an extremely great number of foreign matter when they are minutely inspected. When the hydrogenated products of an aromatic vinyl polymers containing these foreign matter in plenty are molded into moldings such as optical parts such as optical lenses, and substrates for information recording media such as optical disk substrates and magnetic disk substrates, the performance and functions of the resulting moldings are seriously and adversely affected, since these fine foreign matter is not compatible with the hydrogenated products of an aromatic vinyl polymers.
In the case of, for example, an optical lens, a haze value becomes great when the fine foreign matter is contained in plenty, and so the lens tends to become a state that an opaque haze hangs on the surface or in the interior of the lens. When the fine foreign matter is present in plenty in the case of the optical disk, it forms the case of noise and signal error upon reproduction of a signal. A high-capacity optical information recording medium such as DVD (digital video disk) is extremely greater in recording density than the conventional CD (compact disk) and LD (laser disk), and the spot diameter of a laser beam used in recording and reading of information is also extremely small. Accordingly, even the fine foreign matter in the optical disk substrate tends to cause an error, and a bit error rate tends to become great. When the fine foreign matter is present in plenty in the case of a magnetic disk substrate, these foreign matter appears as a great number of projections on the surface of the substrate. A tracking error is easily caused by the surface projections. When a molding formed of a hydrogenated product of an aromatic vinyl polymer containing these foreign matter in plenty is used as a semiconductor related parts such as a carrier (plastic case) of a silicon wafer, the fine foreign matter occurs out of the molding to easily contaminate the silicon wafer.
It is an object of the present invention to provide a molding material capable of providing a substrate for information recording medium having a sufficiently small birefringence value and excellent mechanical strength in combination.
Another object of the present invention is to provide a hydrogenated polymer and a hydrogenated polymer resin composition as molding materials which can provide a substrate having a sufficiently small birefringence value and excellent mechanical strength and moisture resistance, and are also excellent in molding and processing ability, and a substrate for information recording media obtained by molding such a resin material.
A further object of the present invention is to provide a high-quality hydrogenated product of an aromatic vinyl polymer, which is extremely little in the content of fine foreign matter having no compatibility with the polymer.
The present inventors have carried out an extensive investigation with a view toward achieving the above objects. As a result, it has been found that substrates for information recording media molded from a specific hydrogenated polymer having a molecular weight within a specific range and a narrow molecular weight distribution and highly hydrogenated at its aromatic ring portion not only have a sufficiently small birefringence, but also are excellent in mechanical strength. It has further been. found that the above-described hydrogenated polymer the content of a component having a molecular weight (M) of at most 10,000 in which is not higher than a certain level, or a resin composition containing the hydrogenated polymer and a specific compounding additive can be molded into moldings excellent in moisture resistance such as anti-whitening property under high-temperature and high-humidity environment and surface smoothness in addition to the above-described properties.
In addition, it has been found that when the content of foreign matter having a particle diameter of at least 0.5 xcexcm contained in a hydrogenated product of an aromatic vinyl polymer is reduced to 3.0xc3x97104 particles/g or lower, a molding material suitable for use in optical parts excellent in transparency, heat resistance and low moisture absorption property, small in birefringence and markedly improved in haze value can be provided.
The resin materials containing the hydrogenated product according to the present invention is most suitable for use as a material for optical parts, in particular, a material for substrates for information recording media. The present inventors have been led to completion of the present invention on the basis of these findings.
According to the present invention, there is thus provided a hydrogenated polymer obtained by hydrogenating an aromatic vinyl polymer, wherein the hydrogenated polymer has the following features:
(a) the hydrogenation rate of the aromatic rings thereof is at least 97%;
(b) a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is at most 2.0;
(c) the weight average molecular weight (Mw) is 100,000 to 300,000; and
(d) the content of a component having a molecular weight (M) of at most 10,000 is at most 2% by weight based on the total weight of the polymer.
According to the present invention, there is also provided a resin composition comprising the hydrogenated polymer described above and an anti-whitening agent.
According to the present invention, there is further provided a process for producing a substrate for information recording media, which comprises molding a resin material containing the hydrogenated polymer described above into the form of a substrate.
According to the present invention, there is still further provided a hydrogenated polymer obtained by hydrogenating an aromatic vinyl polymer, wherein the content of foreign matter having a particle diameter of at least 0.5 xcexcm in the hydrogenated polymer is at most 3.0xc3x97104 particles/g.
According to the present invention, there is yet; still further provided a substrate for information recording media, which is obtained by molding a resin material comprising a hydrogenated polymer obtained by hydrogenating an aromatic vinyl polymer and having the following features:
a) the hydrogenation rate of the aromatic rings thereof is at least 97%;
b) a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is at most 2.0;
c) the weight average molecular weight (Mw) is 100,000 to 300,000; and
d) the content of a component having a molecular weight (M) of at most 10,000 is at most 2% by weight based on the total weight of the polymer.
 less than Molding Material for Substrate for Information Recording Medium greater than 
The molding material according to the present invention for a substrate for information media is a resin material composed of any of:
(1) a hydrogenated polymer obtained by hydrogenating an aromatic vinyl polymer, wherein the hydrogenation rate of the aromatic rings thereof is at least 97%, a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is at most 2.0, and the weight average molecular weight (Mw) is 100,000 to 300,000;
(2) the above-described hydrogenated polymer (1) the content of a component having a molecular weight (M) of at most 10,000 in which is at most 2% by weight based on the total weight of the polymer;
(3) a resin composition comprising the above-described hydrogenated polymer (2) and an anti-whitening agent; and (4) a hydrogenated polymer the content of foreign matter having a particle diameter of at least 0.5 xcexcm in which is at most 3.0xc3x97104 particles/g.
 less than Hydrogenated Polymer greater than 
The hydrogenated polymer according to the present invention is obtained by hydrogenating the aromatic rings in an aromatic vinyl polymer. The hydrogenation rate of the aromatic rings in the hydrogenated polymer according to the present invention is 97% or higher, preferably 98% or higher, more preferably 99% or higher based on the whole aromatic ring in the aromatic vinyl polymer. If the hydrogenation rate of the aromatic rings is extremely low, the birefringence of the resulting hydrogenated polymer becomes great. It is hence not preferable to conduct the hydrogenation at such a low hydrogenation rate. The hydrogenation rate of the aromatic rings can be determined by a 1H-NMR measuring method.
The weight average molecular weight (Mw) of the hydrogenated product of the aromatic vinyl polymer is within a range of generally 10,000 to 300,000, preferably 100,000 to 270,000, more preferably 100,000 to 250,000: in terms of polystyrene as measured by gel permeation chromatography (GPC). The molecular weight distribution of the hydrogenated product of the aromatic vinyl polymer is expressed by a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn), both, in terms of polystyrene as measured by GPC and is at most 2.0, preferably at most 1.7, more preferably at most 1.3. If the Mw/Mn of the hydrogenated product of the aromatic vinyl polymer is extremely high, the resulting molding material is deteriorated in mechanical strength, and so any satisfactory molding cannot be provided. In addition, such problems that the birefringence becomes great are caused. If the weight average molecular weight (Mw) is extremely low, the mechanical strength of the resulting molding material is deteriorated, and so any satisfactory molding cannot be provided. If the weight average molecular weight (Mw) is extremely high on the other hand, the molding ability of the resulting molding material is deteriorated, and the birefringence thereof becomes great. It is hence not preferable to use any hydrogenated polymer having such a low or high weight average molecular weight.
In a preferred hydrogenated product of an aromatic vinyl polymer in the present invention, the content of a component having a molecular weight (M) of at most 10,000 in the polymer is controlled to at most 2% by weight, preferably at most 1.5% by weight, more preferably at most 1% by weight based on the total weight of the polymer. The content of the component having a molecular weight (M) of at most 10,000 is controlled within the above range, whereby the surface smoothness of a molding obtained by molding such a hydrogenated product of the aromatic vinyl polymer is improved and exhibits excellent performance as an optical part, in particular, a substrate for information recording media.
The aromatic vinyl polymer used as a raw material is a polymer in which a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is generally at most 2.0, the weight average molecular weight (Mw) is 100,000 to 400,000, preferably 100,000 to 300,000, more preferably 100,000 to 280,000.
If the weight average molecular weight (Mw) of the aromatic vinyl polymer used as a raw material is extremely high, it is difficult to conduct the hydrogenation reaction of the aromatic rings at a high hydrogenation rate, and a molecular chain scissoring reaction, which is a competitive reaction, proceeds if the hydrogenation reaction is allowed to proceed until the hydrogenation rate reaches about 100%, so that the molecular weight distribution of the resulting hydrogenated product becomes wider, and the strength properties and heat resistance thereof are lowered because a low-molecular weight component increases. If the weight average molecular weight (Mw) is extremely low on the other hand, the strength properties of the polymer are deteriorated, and so it is difficult to provide any satisfactory molding. It is hence not preferable to use any aromatic vinyl polymer having such a low or high weight average molecular weight.
No particular limitation is imposed on the production process of the aromatic vinyl polymer used as a raw material. However, the polymer can be obtained by, as a preferred process, for example, (co)polymerizing an aromatic vinyl compound or an aromatic vinyl compound and a monomer copolymerizable therewith in a hydrocarbon solvent.
(1) Aromatic Vinyl Compound:
No particular limitation is imposed on the aromatic vinyl compound so far as it is a compound having an aromatic ring and a polymerizable vinyl group. Typical examples of the aromatic vinyl compound include those represented by the following formula: 
wherein R1 represents a hydrogen atom or an alkyl group, and R2 to R6 represent, independently of one another, a hydrogen atom, an alkyl group or a halogen atom.
The alkyl group represented by R1 in the formula is preferably a lower alkyl group having 1 to 5 carbon atoms, and specific examples thereof include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl and amyl groups. R2 to R6 are preferably hydrogen atoms or alkyl groups, more preferably hydrogen atoms or the same lower alkyl groups as in R1. Examples of the halogen atom in R2 to R6 include fluorine, bromine, chlorine and iodine atoms.
As specific examples of the aromatic vinyl compounds, may be mentioned styrene, xcex1-methylstyrene, xcex1-ethylstyrene, xcex1-propylstyrene, xcex1-isopropylstyrene, xcex1-t-butylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butyl-styrene, 5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene and monofluorostyrene. Among these, styrene and xcex1-methylstyrene are preferred.
These aromatic vinyl compounds may be used either singly or in any combination thereof.
(2) Copolymerizable Monomer:
No particular limitation is imposed on the monomer copolymerizable with the aromatic vinyl compound so far as it is copolymerizable with the aromatic vinyl compound by a polymerization method such as radical polymerization, anionic polymerization or cationic polymerization. As examples thereof, may be mentioned conjugated diene monomers such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene and 1,3-cyclohexadiene; nitrile monomers such as acrylonitrile, methacrylonitrile and xcex1-chloroacrylonitrile; (meth)acrylic ester monomers such as methyl methacrylate and methyl acrylate; unsaturated fatty acid monomers such as acrylic acid, methacrylic acid and maleic anhydride; polyolefins such as ethylene and propylene; and phenylmaleimide. These monomers copolymerizable with the aromatic vinyl compound may be used either singly or in any combination thereof.
A proportion of the aromatic vinyl monomer used for obtaining the aromatic vinyl polymer is suitably selected as necessary for the end application intended. However, the proportion is generally at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight, most preferably 100% by weight. The birefringence of the resulting hydrogenated product becomes more sufficiently small as the proportion of the aromatic vinyl monomer in the aromatic vinyl polymer increases.
(3) Initiator:
Examples of an initiator used in the polymerization of the aromatic vinyl polymer include organoalkali metals and combination of an organoalkali metal and a Lewis base. Initiators composed of a combinations of an organoalkali metal and a Lewis base are preferred for the purpose of narrowing the molecular weight distribution of the resulting polymer.
Examples of the organoalkali metals include monoorganolithium compounds such as n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium and stilbenelithium; polyfunctional organolithium compounds such as dilithiomethane, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane and 1,3,5-trilithio-benzene; sodium naphthalene; and potassium naphthalene. Among these, the organolithium compounds are preferred, with the monoorganolithium compounds being particularly preferred.
These organoalkali metals may be used either singly or in any combination thereof. The amount of the organo-alkali metal used is suitably selected according to the molecular weight required of the polymer formed. It is generally within a range of 0.05 to 100 mmol, preferably 0.10 to 50 mmol, more preferably 0.15 to 20 mmol per 1100 g of the monomer(s).
The Lewis base is useful in obtaining an aromatic vinyl polymer having a narrow molecular weight distribution. No particular limitation is imposed on the Lewis base so far as it is that commonly used in solution polymerization, and examples thereof include ether compounds; tertiary amine compounds such as tetramethylethylenediamine, trimethylamine, triethylamine and pyridine; alkali metal alkoxides such as potassium t-amyloxide and potassium t-butoxide; and phosphine compounds such as triphenylphosphine. Among these, the ether compounds are particularly preferred in that the molecular weight distribution (Mw/Mn) of the resulting aromatic vinyl polymer can be sufficiently narrowed.
No particular limitation is imposed on the ether compounds. However, those having generally 2 to 100 carbon atoms, preferably 4 to 50 carbon atoms, more preferably 4 to 20 carbon atoms are preferably used. Specific examples thereof include aliphatic monoethers such as dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, diamyl ether, diisoamyl ether, methyl ethyl ether, methyl propyl ether, methyl isopropyl ether, methyl butyl ether, methyl isoamyl ether, ethyl propyl ether, ethyl isopropyl ether and ethyl butyl ether; aromatic monoethers such as anisole, phenetole, diphenyl ether and dibenzyl ether; cyclic monoethers such as tetrahydrofuran and tetrahydropyran; alkylene glycol dialkyl ethers such as ethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, diethylene glycol diamyl ether, ethylene glycol dioctyl ether, propylene glycol dimethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dibutyl ether, isopropylene glycol dimethyl ether, isopropylene glycol diethyl ether, butylene glycol dimethyl ether, butylene glycol diethyl ether and butylene glycol dibutyl glycol; alkylene glycol alkyl aryl ethers such as ethylene glycol methyl phenyl ether; alkylene glycol diaryl ethers such as ethylene glycol diphenyl ether; and alkylene glycol diaralkyl ethers such as ethylene glycol dibenzyl ether.
These Lewis bases may be suitably used either singly or in any combination thereof. The amount of these Lewis bases used is within a range of 0.001 to 10.0 mmol, preferably 0.01 to 5.0 mmol, more preferably 0.1 to 2.0 mmol per 1 mol of the organoalkali metal used.
(4) Solvent:
No particular limitation is imposed on the hydrocarbon solvent used in the polymerization of the aromatic vinyl polymer so far as it can dissolve a polymer formed and does not deactivate the initiator. Examples thereof include aliphatic hydrocarbons such as n-butane, n-pentane, isopentane, n-hexane, n-heptane and isooctane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane and decalin; and, aromatic hydrocarbons such as benzene and toluene.
Among these, the use of an aliphatic hydrocarbon or alicyclic hydrocarbon is preferred because the hydrogenation reaction can be conducted as it is after the polymerization. These hydrocarbon solvents may be used either singly or in any combination thereof in an amount sufficient for the concentration of the monomer to amount to generally 1 to 30% by weight.
(5) Polymerization conditions:
The polymerization reaction of the aromatic vinyl polymer may be either an isothermal reaction or an adiabatic reaction, and is carried out in a polymerization temperature range of generally 0 to 150xc2x0 C, preferably 20 to 120xc2x0 C. The polymerization time is within a range of generally 0.01 to 20 hours, preferably 0.1 to 10 hours.
After the polymerization reaction, the polymer can be recovered by the publicly known method such as steam stripping, direct desolvating or alcoholic solidifying. In the present invention, the polymer may be fed to a hydrogenating process as it is without recovering the polymer from a polymer solution when a solvent inert to the hydrogenation reaction is used upon the polymerization.
(6) Hydrogenation:
No particular limitation is imposed on the hydrogenation of the aromatic vinyl polymer so far as the hydrogenation is carried out in accordance with a hydrogenation process, by which the hydrogenation rate of aromatic rings is high, and a polymer chain is scarcely scissored, and as an example thereof, may be mentioned a process conducted by using a hydrogenation catalyst containing at least one metal selected from nickel, cobalt, iron, titanium, rhodium, palladium, platinum, ruthenium and rhenium in an organic solvent. Among these hydrogenation catalysts, a nickel catalyst is preferred because a hydrogenated product having a small Mw/Mn is provided. The hydrogenation catalyst may be either a heterogeneous catalyst or a homogeneous catalyst.
The heterogeneous catalyst may be used in the form of a metal or metal compound as it is, or by supporting it on a proper carrier. Examples of the carrier include active carbon, silica, alumina, calcium carbonate, titania, magnesia, zirconia, diatomaceous earth and silicon carbide. Among these, the use of diatomaceous earth is preferred because the molecular weight distribution of the resulting hydrogenated product can be more narrowed. In this case, the amount of the metal supported on the carrier is within a range of generally 0.01 to 80% by weight, preferably 0.05 to 60% by weight.
As the homogeneous catalyst, there may be used a catalyst obtained by combining nickel, cobalt, titanium or iron compound with a organometallic compound such as an organoaluminum or organolithium compound; or an organometallic complex of rhodium, palladium, platinum, ruthenium, rhenium or the like. Examples of the nickel, cobalt, titanium or iron compound used in the homogeneous catalyst include acetylacetone salts, naphthenates, cyclopentadienyl compounds and cyclopentadienyldichloro compounds of these various metals. Examples of the organoaluminum compound include alkylaluminums such as triethylaluminum and triisobutylaluminum; alkylaluminum halides such as diethylaluminum chloride and ethylalumlnum dichloride; and alkylaluminum hydrides such as diisobutylaluminum hydride. Examples of the organometallic complex include xcex3-dichloro-xcfx80-benzene complexes, dichloro-tris(triphenylphosphine) complexes and hydridochloro-tris(triphenylphosphine) complexes of the respective metals mentioned above.
These hydrogenation catalyst may be used either singly or in any combination thereof. The amount of the hydrogenated catalyst used is within a range of generally 0.03 to 50 parts by weight, preferably 0.16 to 33 parts by weight, more preferably 0.33 to 15 parts by weight per 100 parts by weight of the aromatic vinyl polymer.
Examples of the organic solvent used in the hydrogenation process include the aliphatic hydrocarbons described above; the alicyclic hydrocarbons described above; ethers such as tetrahydrofuran and dioxane; alcohols; and esters. These organic solvents may be used either singly or in any combination thereof. The amount of the organic solvent used is within a range sufficient for the concentration of the aromatic vinyl polymer to amount to generally 1 to 50% by weight, preferably 3 to 40% by weight, more preferably 5 to 30% by weight.
The hydrogenation reaction is performed at a temperature within a range of generally 10 to 250xc2x0 C., preferably 50 to 200xc2x0 C., more preferably 80 to 180xc2x0 C. under a hydrogen pressure within a range of generally 1 to 300 kg/cm2, preferably 10 to 250 kg/cm2, more preferably 20 to 200 kg/cm2.
 less than Resin Composition greater than 
The resin composition according to the present invention comprises a hydrogenated polymer, wherein the hydrogenation rate of the aromatic rings thereof is at least 97%, a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is at most 2.0, the weight average molecular weight (Mw) is 100,000 to 300,000, and the content of a component having a molecular weight (M) of at most 10,000 is at most 2% by weight based on the total weight of the polymer, and an anti-whitening agent.
For use application to substrates for information recording media, there may be used a resin composition comprising a hydrogenated product of an aromatic vinyl polymer, wherein the hydrogenation rate of the aromatic rings thereof is at least 97%, a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight.(Mn) is at most 2.0, and the weight average molecular weight (Mw) is 100,000 to 300,000, and an anti-whitening agent.
This resin composition is used as a molding material, whereby moldings excellent in anti-whitening effect and molding and processing ability can be provided.
The anti-whitening effect means a property that the resulting molding undergoes no whitening under high-temperature and high-humidity environment or in a steam test. The molding and processing ability means a property that a molding little in defects such as irregularities on the surface of the molding, and surface imperfection such as silver streaks and voids, and hence excellent in surface smoothness can be provided.
 less than Anti-whitening Agent greater than 
The anti-whitening agent used in the present invention is a substance capable of imparting an anti-whitening effect, i.e., a function that whitening of a molding formed of the hydrogenated polymer can be prevented under high-temperature and high-humidity environment or in a steam test when it is incorporated in a certain amount into the hydrogenated product of the aromatic vinyl polymer.
Such an anti-whitening agent includes at least one substance selected from the group consisting of other polymers than the hydrogenated products of the aromatic vinyl polymers, partially etherified compounds of polyhydric alcohols, partially esterified compounds of polyhydric alcohols and finely particulate fillers.
(1) Other Ppolymers than the Hydrogenated Products of the Aromatic Vinyl Polymers:
No particular limitation is imposed on polymers capable of being incorporated into the hydrogenated products of the aromatic vinyl polymers in the present invention so far as they are polymers capable of imparting an anti-whitening effect when they are incorporated into the hydrogenated products of the aromatic vinyl polymers according to the present invention. However, the polymer is preferably such that when the polymer is incorporated into the hydrogenated product of the aromatic vinyl polymer, the form of the polymer before incorporation changes to form, for example, a microdomain state, whereby the polymer can be dispersed in the hydrogenated polymer.
Such polymers include soft polymers such as rubbery polymers and thermoplastic elastomers, and resins.
Specific examples of the resins include polyether or polythioether polymers such as poly(phenylene sulfide) and poly(phenylene ether); polyester polymers such as aromatic polyester, polyarylate, polyethylene terephthalate, polybutylene terephthalate, polycarbonate and poly(ether ketone); linear polyolefin polymers such as polyethylene, polypropylene and poly(4-methylpentene-1); general-purpose transparent resins such as polymethyl methacrylate, copolymers cyclohexyl methacrylate and methyl methacrylate and acrylonitrile-styrene copolymers (AS resins); acrylic resins; MS resins; and liquid crystal plastics.
The soft polymers used in the present invention are polymers having a glass transition temperature of 40xc2x0 C. or lower and include ordinary rubbery polymers and thermoplastic elastomers. Incidentally, when rubbery polymers obtained by block copolymerization, and the like have at least two glass transition temperatures, they may be used as the soft polymers so far as the lowest glass transition temperature thereof is 40xc2x0 C. or lower.
Specific examples of the rubbery polymers include isoprene rubber and hydrogenated products thereof; chloroprene rubber and hydrogenated products thereof; saturated polyolefin rubbers such as ethylene propylene copolymers, ethylene-xcex1-olefin copolymers and propylene. xcex1-olefin copolymers; diene copolymers such as ethylene.propylene.diene terpolymers, xcex1-olefin.diene copolymers, diene copolymers, isobutylene.isoprene copolymers and isobutylene.diene copolymers, halides thereof, and hydrogenated products of the diene copolymers and halides thereof; acrylonitrile.butadiene copolymers and hydrogenated products thereof; fluorine-containing rubbers such as vinylidene fluoride.ethylene trifluoride copolymers, vinylidene fluoride.propylene hexafluoride copolymers, vinylidene fluoride.propylene hexafluoride.ethylene tetrafluoride terpolymers and propylene.ethylene tetrafluoride copolymers; special rubbers such as urethane rubber, silicone rubber, polyether rubber, acrylic rubber, chlorosulfonated polyethylene rubber, epichlorohydrin rubber, propylene oxide rubber and ethylene.acrylic rubber; norbornene rubbery polymers such as copolymers of a norbornene monomer and ethylene or an xcex1-olefin, terpolymers of a norbornene monomer, ethylene and an xcex1-olefin, ring-opening polymers of norbornene monomers and hydrogenated products of ring-opening polymers of norbornene monomers; random copolymers such as styrene.butadiene rubber and high-impact styrene rubber obtained by emulsion polymerization or solution polymerization, and hydrogenated product thereof.
Specific examples of the thermoplastic elastomers include thermoplastic styrene elastomers such as linear or radial block copolymers of an aromatic vinyl monomer and a conjugated diene monomer, such as styrene.butadiene.styrene rubber, styrene.isoprene.styrene rubber and styrene ethylene butadiene styrene rubber, and hydrogenated products thereof; thermoplastic urethane elastomers; thermoplastic polyamide elastomers; thermoplastic 1,2-polybutadiene elastomers; thermoplastic vinyl chloride elastomers; and fluorine-containing thermoplastic elastomers.
Among these, the copolymers of an aromatic vinyl monomer and a conjugated diene monomer, and hydrogenated products thereof are preferred because they are good in dispersibility in the hydrogenated products of the aromatic vinyl polymers. The copolymers of an aromatic vinyl monomer and a conjugated diene monomer may be either black copolymers or random copolymers. The copolymers are more preferably hydrogenated at their unsaturated portions other than the aromatic rings from the viewpoint of weather resistance. Specific examples thereof include styrene-butadiene block copolymers, styrene.butadiene.styrene block copolymers, styrene.isoprene block copolymers, styrene.isoprene.styrene block copolymers and hydrogenated products thereof, and styrene.butadiene random copolymers and hydrogenated products thereof.
When the above-described polymer is added, many dispersed microdomains are formed in the resulting moldings in many cases. The average particle diameter (determined by measuring the length and breadth of each of 100 microdomains selected at random by observation through an electron microscope, calculating a microdomain diameter from the measured value in accordance with the expression [(length+breadth)/2] and taking an average of the calculated values) is generally 0.001 to 0.5 xcexcm, preferably 0.005 to 0.3 xcexcm, particularly preferably 0.01 to 0.2 xcexcm. The formation of such microdomains is preferred because the resulting molding is balanced between transparency and anti-whitening effect under high-temperature and high-humidity environment at a high level.
(2) Partially Etherified Compound and Partially Esterified Compound:
The partially etherified compound used in the present invention is an organic compound having at least one alcoholic hydroxyl group and at least one ether linkage. The partially esterified compound is an organic compound having at least one alcoholic hydroxyl group and at least one ester linkage. The partially etherified compound or partially esterified compound is incorporated into the hydrogenated product of the aromatic vinyl polymer, whereby whitening under high-temperature and; high-humidity environment can be prevented, and high transparency can be retained.
No particular limitation is imposed on the organic compound having at least one alcoholic hydroxyl group and at least one ether linkage so far as it is an organic compound having at least one alcoholic hydroxyl group, not a phenolic hydroxyl group, and at least one ether linkage unit in its molecule. The partially etherified compound is such a compound that at least one of hydroxyl groups in a polyhydric alcohol has been etherified. The polyhydric alcohol has at least 2, preferably at least 3, more preferably 3 to 8 hydroxyl groups.
No particular limitation is imposed on the organic compound having at least one alcoholic hydroxyl group and at least one ester linkage so far as it is an organic compound having at least one alcoholic hydroxyl group, not a phenolic hydroxyl group, and at least one ester linkage unit in its molecule. The partially esterified compound is such a compound that at least one of hydroxyl groups in a polyhydric alcohol has been esterified. The polyhydric alcohol has at least 2, preferably at least 3, more preferably 3 to 8 hydroxyl groups.
Specific examples of the polyhydric alcohol include polyethylene glycol, glycerol, trimethylolpropane, pentaerythritol, diglycerol, triglycerol, dipentaerythritol, 1,6,7-trihydroxy-2,2-di(hydroxy-methyl)-4-oxoheptane, sorbitol, 2-methyl-1,6,7-trihydroxy-2-hydroxymethyl-4-oxoheptane, 1,5,6-trihydroxy-3-oxohexane pentaerythritol and tris(2-hydroxy-ethyl)isocyanulate. Among these, trihydric or still higher polyhydric alcohols, particularly polyhydric alcohol having 3 to 8 hydroxyl groups are preferred. In order to obtain the partially esterified compound, glycerol, diglycerol, triglycerol or the like capable of synthesizing a partially esterified compound containing an xcex1,xcex2-diol is preferred.
Specific examples of such partially etherified compounds and partially esterified compounds include etherified products and esterified products of polyhydric alcohols, such as glycerol monostearate, glycerol monolaurate, glycerol monobehenate, diglycerol monostearate, glycerol distearate, glycerol dilaurate, pentaerythritol monostearate, pentaerythritol monolaurate, pentaerythritol monobehenate, pentaerythritol distearate, pentaerythritol dilaurate, pentaerythritol tristearate and dipentaerythritol distearate; 3-(octyloxy)-1,2-propanediol, 3-(decyloxy)-1,2-propanediol, 3-(lauryloxy)-1,2-propanediol, 3-(4-nonylphenyloxy)-1,2-propanediol, 1,6-dihydroxy-2,2-di(hydroxymethyl)-7-(4-nonylphenyloxy)-4-oxoheptane, ether compounds obtained by a reaction of a condensate of p-nonylphenyl ether with formaldehyde with glycidol, ether compounds obtained by a reaction of a condensate of p-octylphenyl ether with formaldehyde with glycidol and ether compounds obtained by a reaction of a condensate of p-octylphenyl ether with dicyclopentadiene with glycidol.
These partially etherified compounds and partially esterified compounds of the polyhydric alcohols may be used either singly or in any combination thereof.
No particular limitation is imposed on the molecular weights of these partially etherified compounds and partially esterified compounds of the polyhydric alcohols. However, a compound having a molecular weight of generally 500 to 2,000, preferably 800 to 1,500 is preferred because the transparency of the resulting molding material is scarcely deteriorated.
(3) Finely Particulate Filler:
The finely particulate fillers used in the present invention include organic and inorganic fillers. However, no particular limitation is imposed on the filler so far as it is that commonly used in polymer industries.
These finely particulate fillers are such that when they are incorporated into the hydrogenated product of the aromatic vinyl polymer (hydrogenated polymer), they are dispersed in the hydrogenated polymer in the finely particulate state before incorporation without changing the form thereof. Therefore, even when the composition of a filler is the same as that of the above-described another polymer than the hydrogenated polymers, the filler is said finely particulate filler so far as it can be dispersed in the hydrogenated polymer while retaining the finely particulate form before incorporation.
As the organic filler, may be used general organic polymer particles or crosslinked organic polymer particles. Specific examples thereof include particles or crosslinked particles of polyolefins such as polyethylene, polypropylene, poly(methyl-1-butene), poly(4-methyl-1-pentene) and poly(l-butene); halogen-containing vinyl polymers such as polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polychloroprene and chlorinated rubber; (co)polymers derived from xcex1,xcex2-unsaturated acids or derivatives thereof, such as polyarylate, polymethacrylate, polyacrylamide, polyacrylonitrile, acrylonitrile.butadiene.styrene terpolymers, polyacrylonitrile and acrylonitrile styrene.acrylic ester terpolymers; polymers derived from an unsaturated alcohol and an amine or acyl derivative or acetal thereof, such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stealate, polyvinyl benzoate, polyvinyl maleate, polyvinyl butyral, polyallyl phthalate, polyallylmelamine and ethylene.vinyl acetate copolymers; polymers derived from polyethylene oxides or bisglycidyl ethers; polyphenylene oxide; polycarbonate; polysulfone; polyurethane; urea resins; polyamides such as nylon 6, nylon 66, nylon 11 and nylon 12; polyesters such as polyethylene terephthalate, polybutylene terephthalate and poly(1,4-dimethylol cyclohexane terephthalate); polymers derived from aldehyde and phenol, urea or melamine and having a crosslinked structure, such as phenol.formaldehyde resins, urea.formaldehyde resin and melamine.formaldehyde resins; and natural high-molecular weight compounds, for example, cellulose acetate, cellulose propionate, cellulose ether, etc.
Examples of the inorganic fillers include oxides, hydroxides, sulfides, nitrides, halides, carbonates, sulfates, acetates, phosphates, phosphates, organic carboxylates, silicates, titanates and borates of elements of Groups 1, 2, 4, 6, 7, 8 to 10, 11, 12, 13 and 14, and hydrates or complex compounds thereof; and natural mineral particles. Specific examples thereof include particles of compounds of elements of Group 1, such as lithium fluoride and borax (sodium borate hydrate); compounds of elements of Group 2, such as magnesium carbonate, magnesium phosphate, magnesium oxide, magnesium chloride, magnesium acetate, magnesium fluoride, magnesium titanate, magnesium silicate, magnesium silicate hydrate (talc), calcium carbonate, calcium phosphate, calcium phosphate, calcium sulfate (gypsum), calcium acetate, calcium terephthalate, calcium hydroxide, calcium silicate, calcium fluoride, calcium titanate, strontium titanate, barium carbonate, barium phosphate, barium sulfate and barium phosphite; compounds of elements of Group 4, such as titanium dioxide (titania), titanium monoxide, titanium nitride, zirconium dioxide (zirconia) and zirconium monoxide; compounds of elements of Group 6, such as molybdenum dioxide, molybdenum trioxide and molybdenum sulfide; compounds of elements of Group 7, such as manganese chloride and manganese acetate; compounds of elements of Groups 8 to 10, such as cobalt chloride and cobalt acetate; compounds of elements of Group 11, such as copper(1) iodide; compounds of elements of Group 12, such as zinc oxide and zinc acetate; compounds of elements of Group 13, such as aluminum oxide (alumina), aluminum fluoride and aluminosilicate (alumina silicate, kaolin, kaolinite); compounds of elements of Group 14, such as silicon oxide (silica, silica gel), black lead, carbon, graphite and glass; and natural minerals such as carnallite, kinite, mica (mica, phlogopite) and pyrosmalite.
The average particle diameter of the inorganic filler is within a range of generally 0.05 to 50 xcexcm, preferably 0.1 to 30 xcexcm in terms of an average particle diameter determined from diameters of 3,000 to 5,000 particles by observation through an electron microscope. Spherical particles that a ratio (length/breadth) of the length to the breadth is at most 2 are preferred to needle particles. When the size of the filler falls within this range, the transparency can be balanced with the anti-whitening effect under high-temperature and high-humidity environment at a high level.
Among these anti-whitening agents, the soft polymers, partially etherified compounds and partially esterified compounds are preferred because the transparency, heat resistance, and molding and processing ability of the resulting resin composition can be balanced with the anti-whitening effect under high-temperature and high-humidity environment at a high level.
In the present invention, the anti-whitening agent described above is incorporated in a proper amount into the hydrogenated product of the aromatic vinyl polymer. The amount of this agent incorporated is determined according to the combination of the hydrogenated product of the aromatic vinyl polymer and the anti-whitening agent. If the amount incorporated is too great, the glass transition temperature and transparency of the resulting resin composition are greatly deteriorated, and so the resin composition becomes unsuitable for use as an optical material. If the amount incorporated is too small on the other hand, the resulting moldings may undergo whitening in some cases.
The amount of the anti-whitening agent incorporated is generally 0.01 to 10 parts by weight, preferably 0.02 to 5 parts by weight, more preferably 0.05 to 2 parts by weight per 100 parts by weight of the hydrogenated product of the aromatic vinyl polymer. The amount incorporated within the above range is preferred because the heat resistance and transparency of the resulting molding are balanced with the anti-whitening effect under high-temperature and high-humidity environment at a high-level.
When a resin composition, in which the partially etherified compound or partially esterified compound of the polyhydric alcohol among the above-described anti-whitening agents is incorporated, is used to mold a substrate for information recording media, and a recording film layer for information recording is formed on the substrate, besides the anti-whitening effect under high-temperature and high-humidity environment, deterioration of adhesion of the recording film layer under high-temperature and high-humidity environment, partially separating phenomena such as blister, corrosion of the recording film layer, etc. can be prevented. Therefore, such a resin composition is useful.
 less than Hydrogenated Product of Aromatic Vinyl Polymer Containing Little Foreign Matter greater than 
The high-quality hydrogenated product of the aromatic vinyl polymer containing little foreign matter according to the present invention is a hydrogenated polymer the content of foreign matter having a particle diameter of at least 0.5 xcexcm in which is at most 3.0xc3x97104 particles/g. The term xe2x80x9cforeign matterxe2x80x9d as used herein means impurities (contaminants), catalyst residue, gelled products, etc. mixed in the form of fine particle, fiber, plate or the like into the hydrogenated polymer without being compatibilized therewith. The content of the foreign matter having a particle diameter of at least 0.5 xcexcm is a value determined by subjecting an organic solvent solution of the hydrogenated polymer at a concentration of 1.5% by weight to measurement by means of a light scattering type fine particle detector.
The cyclic hydrocarbon polymer according to the present invention contains foreign matter having a particle diameter of at least 0.5 xcexcm in an amount of at most 3xc3x97104 particles/g, preferably at most 2.0xc3x97104 particles/g. In use application to optical disk substrates of which particularly high transparency (low haze) and low bit error rate are required, the content of foreign matter having a particle diameter of at least 0.5 xcexcm can be reduced to preferably at most 1.0xc3x97104 particles/g, more preferably at most 7.0xc3x97103 particles/g, particularly preferably at most 5.0xc3x97103 particles/g. The lower limit of the content of foreign matter having a particle diameter of at least 0.5 xcexcm is generally about 0.1xc3x97103 particles/g, often about 0.5xc3x97103 particles/g from the viewpoint of treatment efficiency of foreign matter removal.
The content of foreign matter in the hydrogenated polymer can be determined by means of the light scattering fine particle detector. The form of the foreign matter is generally spherical. However, the form is not limited thereto. The details of the foreign matter include all substances incompatible with cyclic hydrocarbon polymers such as catalyst residues, gelled products and by-products, including impurities mixed in from the outside. Those substances,having a particle diameter of at least 0.5 xcexcm as measured by means of the light scattering fine particle detector are regarded as foreign matter, and the content thereof is determined.
In the high-quality hydrogenated polymer containing little foreign matter according to the present invention, the weight average molecular weight (Mw) is preferably adjusted within a range of 100,000 to 300,000, more preferably 100,000 to 270,000, particularly preferably 100,000 to 250,000 in terms of polystyrene as measured by GPC in order to balance it among various properties such as strength properties, moldability and birefringence at a high level. In order to improve the mechanical strength and heat resistance in particular at a high level, the molecular weight distribution (Mw/Mn) thereof is preferably at most 2.0, more preferably at most 1.7, particularly preferably at most 1.3. A hydrogenated polymer the content of a component having a molecular weight (M) of at most 10,000 in which is at most 2% by weight based on the total weight of the polymer is further preferred.
The hydrogenated polymer containing little foreign matter according to the present invention contains a volatile component in an amount of generally at most 0.3% by weight, preferably at most 0.1% by weight, more preferably at most 500 ppm. In order to provide a particularly high-quality molding, the content of the volatile component is preferably reduced to at most 500 ppm, more preferably at most 300 ppm, particularly preferably at most 200 ppm. Examples of the volatile component include organic solvents, unreacted monomers or modified products thereof, etc. When a hydrogenated polymer containing the volatile component in a too great amount is molded into a thin molding such as an optical disk substrate by injection molding, the resultant molding tends to cause silver streaks and voids.
 less than Removal Method of Foreign Matter greater than 
No particular limitation is imposed on the method for removing foreign matter from the hydrogenated product of the aromatic vinyl polymer (hydrogenated polymer). However, as a preferred method for removing the foreign matter, may be mentioned a method comprising filtering a solution containing the hydrogenated polymer through a mechanical filter or a filter having an electrostatically capturing function. After the filtering process, the filtrate is preferably concentrated and dried to remove the volatile component.
(1) Filtration Process:
As examples of the method for filtering the solution containing the hydrogenated polymer, may be mentioned (a) a method comprising filtering the solution at least twice through a mechanical filter having a pore size of at most 0.5 xcexcm, preferably at most 0.3 xcexcm, and (b) a method comprising filtering the solution through a filter having an electrostatically capturing function. Among these methods, the method (b) making use of the filter having the electrostatically capturing function is preferred because it has a high capability of removing ultrafine foreign matter to remove the ultrafine foreign matter which cannot be captured by filtration through the mechanical filter depending on pore openings, and can prevent foreign matte from regenerating by reaggregation after the filtration.
As the solution containing the hydrogenated polymer, the reaction solution after the hydrogenation reaction is used as it is. However, a process for removing the catalyst from the reaction solution may be provided before this filtration process. The concentration of the solution upon the filtration is generally 1 to 40% by weight, preferably 5 to 35% by weight, more preferably 10 to 30% by weight. When a hydrogenated polymer collected as a solid polymer after the hydrogenation process is used, the hydrogenated polymer is dissolved in an organic solvent into a solution.
Various kinds of additives such as an antioxidant, other resin components, etc. may be added to the solution of the hydrogenated polymer before the filtration to dissolve them. These additive components may be added after dissolving them in an organic solvent. For example, when an antioxidant is melt-blended with a cyclic hydrocarbon polymer, it is difficult to sufficiently remove ultrafine foreign matter. However, it is blended in a solution state, and the solution is filtered, whereby the foreign matter can be reduced to a great extent.
The filter having the electrostatically capturing function is a filter having a function that charged foreign matter is electrically captured and removed, and a charged filter medium is generally used. In general, a zeta potential filter (xcex6 filter) the zeta potential of which has been controlled is used. As the zeta potential filter, is generally used a filter obtained by applying a positive charge modifier to a filter medium like cellulose fiber/silica/positive charge modifier (polyamine epichlorohydrin resin, aliphatic polyamine or the like) described in Japanese Patent Application Laid-Open (KOHYO) No. 504379/1992 through PCT route, or the like. Examples of other filter media than the above include fiber or membrane filters made of polypropylene, polyethylene, PTFE, etc., fiber filters made of cellulose, glass fiber-made filters, filters made of an inorganic substance such as diatomaceous earth, and metal fiber-made filters. Examples of other positive charge modifiers include melamine-formaldehyde positive ion colloidal and inorganic positive ion colloidal silica. A positive charge modified filter is marketed under the trademark xe2x80x9cZeta Plusxe2x80x9d by Cuno Co. The pore size of the filter having the electrostatically capturing function is generally about 0.5 to 1 xcexcm. The filtration through the filter having the electrostatically capturing function is generally carried out in combination with the mechanical filter because its throughput capacity is not necessarily high. No particular limitation is imposed on the order of the respective filters used. The order is optional like, for example, {circle around (1)} the order of mechanical filter/electrostatically capturing filter/mechanical filter, {circle around (2)} the order of mechanical filter/electrostatically capturing filter, {circle around (3)} the order of electrostatically capturing filter/mechanical filter, and {circle around (4)} the order of mechanical filter/mechanical filter/electrostatically capturing filter.
No particular limitation is imposed on the mechanical filter so far as it is not adversely affected by any solvent. Examples thereof include fiber or membrane filters made of polypropylene, polyethylene, PTFE, etc., fiber filters made of cellulose, glass fiber-made filters, filters made of an inorganic substance such as diatomaceous earth, and metal fiber-made filters. No particular limitation is imposed on the pore size of the mechanical filter, and it is generally at most 10 xcexcm, preferably at most 5 xcexcm, more preferably at most 1 xcexcm. These mechanical filters may be used either singly or in any combination thereof. However, when no filter having the electrostatically capturing function is used in combination, it is desirable that a filter having a pore size of generally at most 0.5 xcexcm, preferably at most 0.3 xcexcm be used as the mechanical filter, and the filtration process be conducted repeatedly at least twice.
(2) Removal Process of Volatile Component:
It is desirable that the filtrate after the filtration be heated under reduced pressure in, for example, a closed system in such a manner that foreign matter is not mixed in from an external environment, to remove the volatile component, and then cooled under an environment high in air cleanliness class such as in the interior of a clean room, for example, under an environment that the air cleanliness class is strictly controlled to at most class 1,000, preferably at most class 100 to pelletize it. More specifically, in order to remove the solvent after the filtration of the solution, it is preferable to adopt a removal method of the organic solvent, by which no foreign matter is mixed in.
The removal of the organic solvent is conducted by heating the solution of the hydrogenated polymer under reduced pressure (concentrating and drying process). Examples of apparatus for this process include centrifugal, thin film, continuous evaporator type dryers such as Kontro (manufactured by Hitachi Ltd.) and Smith type (manufactured by Shinko-Pfaudler Company, Ltd.); scrape surface exchanger type continuous reactor type dryers such as Votator (manufactured by Chemetron Co.) and Onlator (manufactured by Sakura Seisakusho Co., Ltd.), and high viscosity reactors such as SCR (manufactured by Mitsubishi Heavy Industries, Ltd.). The operation conditions of these apparatus are suitably selected. However, the solution after the filtration is generally heated at a temperature of 220 to 300xc2x0 C., preferably 240 to 290xc2x0 C., more preferably 250 to 270xc2x0 C. under a pressure of at most 25 kPa, preferably at most 15 kPa, more preferably at most 5 kPa to remove the volatile component. The operation time is determined to be time sufficient to remove the volatile component. However, it is generally at least 10 minutes. The operation may be conducted under an atmosphere of an inert gas such as nitrogen or argon.
The hydrogenated polymer tends to reduce their molecular weights by thermal decomposition. In the removal process of the volatile component, it is particularly desirable that the content of the volatile component remaining in the hydrogenated polymer be reduced to about several hundreds ppm or lower. When it is attempted to remove the volatile component to such a degree at once by one-stage concentration and drying, however, the temperature of the hydrogenated polymer or the solution is rapidly lowered by latent heat of evaporation, and so the hydrogenated polymer may be partially stuck to cause clogging or vibration of the apparatus in some cases. Therefore, the removal process of the volatile component is preferably performed by a process of two or more stages. Specifically, there may be mentioned a process in which at least 2 concentrating and drying apparatus are used to continuously remove the volatile component (multi-stage concentrating and drying process). In this case, the same kind of concentrating and drying apparatus may be used in each stage, or different kinds of apparatus may be used in combination. As an example of the combination of different apparatus, may be mentioned a process in which a solution of the hydrogenated polymer is introduced, as a first stage, into a vessel, which can conduct heating, but has no stirrer, at a high temperature under a high pressure to evaporate (flash) the volatile component, and the concentrated polymer solution or molten polymer obtained in the first stage is then introduced, as a second stage, into a concentrating and drying apparatus, which can conduct heating and pressure reduction and is equipped with a stirrer, to remove the remaining volatile component.
Specifically, in the first stage, the volatile component such as a solvent is removed until the concentration of the polymer solution reaches generally 30 to 99.5% by weight, preferably 40 to 98% by weight, more preferably 50 to 95% by weight. If the concentration of the hydrogenated polymer in the first stage is intended to excessively raise, the quantity of heat required for evaporation becomes great, and the load of the apparatus is increased. If the concentration of the hydrogenated polymer in the first stage is too low, latent heat of evaporation becomes great, and the amount of the volatile component recovered is also increased, and so the load of the apparatus in the next process is increased. In any case, the concentration and drying is conducted under the above-described conditions in at least a final stage.
In this process, additives such as antioxidants, light stabilizers and ultraviolet absorbents may be added as needed. More specifically, these additives are uniformly dissolved in the polymer solution before the concentration and drying, and the polymer solution can be then concentrated and dried. The content of the foreign matter is reduced as much as possible, however, it is desirable that these additive be added to the polymer solution before the filtration process. The additives such as the antioxidants are preferably not easily vaporized off under conditions for drying.
 less than Additives greater than 
Into the hydrogenated products of the aromatic vinyl polymers according to the present invention, may be incorporated additives such as antioxidants, ultraviolet absorbents, light stabilizer, plasticizers, antistatic agents, lubricants, coloring agents (dyes and pigments), near infrared absorbents and fluorescent whitening agents as needed. Amounts of these additives incorporated are suitably selected within limits not impeding the objects of the present invention.
In particular, the antioxidants are preferably contained in the hydrogenated polymers or resin compositions from the viewpoints of preventing deterioration or decomposition of the hydrogenated polymers and the resin composition containing such a hydrogenated polymer by oxidation upon molding, and oxidation of the resulting moldings under service environment.
Examples of the antioxidants include phenolic antioxidants, phosphorus-containing antioxidants an sulfur-containing antioxidants.
As the phenolic antioxidants, the conventionally known antioxidants may be used, and examples thereof include acrylate type phenol compounds described in Japanese Patent Application Laid-Open Nos. 179953/1988 and 168643/1989, such as 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate and 2,4-di-t-amyl-6-[1-(3,5-di-t-amyl-2-hydroxyphenyl)ethyl]phenyl acrylate; alkyl-substituted phenol compounds such as 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate, 2,2xe2x80x2-methylene-bis(4-methyl-6-t-butylphenol), 4,4xe2x80x2-butylidene-bis(6-t-butyl-m-cresol), 4,4xe2x80x2-thiobis(3-methyl-6-t-butyl-phenol), bis(3-cyclohexyl-2-hydroxy-5-methylphenyl)-methane, 3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-methyl-phenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tetrakis[methylene-3-(3xe2x80x2,5xe2x80x2-di-t-butyl-4xe2x80x2-hydroxyphenyl)propionate]methane [i.e., pentaerythrimethyl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]], triethylene glycol bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] and tocopherol; and triazine group-containing phenolic compounds such as 6-(4-hydroxy-3,5-di-t-butylanilino)-2,4-bisoctylthio-1,3,5-triazine,6-(4-hydroxy-3,5-dimethyl-anilino)-2,4-bisoctylthio-1,3,5-triazine, 6-(4-hydroxy-3-methyl-5-t-butylanilino)-2,4-bisoctylthio-1,3,5-triazine and 2-octylthio-4,6-bis-(3,5-di-t-butyl-4-oxyanilino)-1,3,5-triazine.
No particular limitation is imposed on the phosphorus-containing antioxidant so far as they are commonly used in general resin industries. Examples thereof include monophosphite compounds such as triphenyl phosphite, diphenylisodecyl phosphite, phenyldiisodecyl phosphate, tris(nonylphenyl) phosphite, tris-(dinonylphenyl) phosphite, tris(2,4-di-t-butylphenyl) phosphite, tris(2-t-butyl-4-methylphenyl) phosphite, tris-(cyclohexylphenyl) phosphite, 2,2-methylenebis(4,6-di-t-butylphenyl)octyl phosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(3,5-di-t-butyl-4-hydroxybenzyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene; and diphosphite compounds such as 4,4xe2x80x2-butylidene-bis(3-methyl-6-t-butylphenyl-di-tridecyl phosphate), 4,4xe2x80x2-isopropylidene-bis[phenyl-di-alkyl(C12-C15) phosphate], 4,4xe2x80x2-isopropylidene-bis[diphenylmonoalkyl(C12-2-C15) phosphite], 1,1,3-tris(2-methyl-4-di-tridecyl-phosphite-5-t-butylphenyl)butane, tetrakis(2,4-di-t-butyl-phenyl)-4,4xe2x80x2-biphenylene diphosphite, cyclic neopentane-tetrayl bis(isodecyl phosphite), cyclic neopentanetetrayl bis(nonylphenyl phosphite), cyclic neopentanetetrayl bis(2,4-di-t-butylphenyl phosphite), cyclic neopentanetetrayl bis(2,4-dimethylphenyl phosphate) and cyclic neopentanetetrayl bis(2,6-di-t-butylphenyl phosphate). Among these, the monophosphite compounds are preferred, with tris(nonylphenyl)phosphate, tris(dinonylphenyl) phosphate and tris(2,4-di-t-butylphenyl)phosphate being particularly preferred.
Examples of the sulfur-containing antioxidants include dilauryl 3,3-thiodipropionate, dimyristyl3,3xe2x80x2-thiodipropionate, distearyl 3,3-thiodipropionate, laurylstearyl 3,3-thiodipropionate, pentaerythritol tetrakis(xcex2-lauryl thiopropionate) and 3,9-bis(2-dodecyl-thioethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane.
These antioxidants may be used either singly or in any combination thereof. A proportion of the antioxidant incorporated is within a range of generally from 0.001 to 5 parts by weight, preferably from 0.01 to 1 part by weight per 100 parts by weight of the hydrogenated polymer.
 less than Substrate for Information Recording media greater than 
The substrate for information recording media according to the present invention can be produced by using a resin material composed of the hydrogenated product of the aromatic vinyl polymer (hydrogenated polymer) or the resin composition comprising the hydrogenated polymer to mold it in the form of a substrate by any of the conventional molding methods.
The molding methods include injection molding (injection compression molding), compression molding, press molding, extrusion and cast molding methods, and the like. However, the use of the injection molding (injection compression molding) method is preferred in order to provide a substrate sufficiently small in birefringence and excellent mechanical strength and surface smoothness.
A specific injection molding method includes a method in which the molding material according to the present invention is heated and melted by means of, for example, a heating cylinder, and the molten molding material is charged into a mold and then cooled. A stamper is installed on the inner surface of the mold used to transfer pits, grooves, etc. The form of the substrate is changed according to the standard of the substrate, and the thickness and diameter thereof is generally 0.05 to 10 mm and 30 mm to 300 mm, respectively.
No particular limitation is imposed on the molding conditions. However, it is preferred that the set cylinder temperature of a molding machine be controlled within a range of 200 to 400xc2x0 C., preferably 220 to 380xc2x0 C., most preferably 240 to 360xc2x0 C., and the mold temperature be controlled to 50 to 180xc2x0 C. If the temperatures are too low, the transferability of the molding material is lowered, and the birefringence of the resulting molding becomes great in both cases. If the temperatures are too high, in some cases, the molding cycle may be elongated, burr may occur or the decomposition of the resin may be caused. It is also possible to adjust the temperature of a sprue part to a separate temperature, for example, 30 to 100xc2x0 C.
In order to prevent the oxidation, decomposition and the like of the molding material melted in the cylinder upon the molding, there may be used (A) a method of holding the interiors of the cylinder and mold at a low oxygen concentration state, or (B) a method of removing dissolved oxygen in the molding material before the molding. By using such a method, the surface smoothness and the like of the resulting molding are further enhanced. These molding methods may be applied to not only the hydrogenated products of the aromatic vinyl polymers according to the present invention, but also the conventionally known alicyclic structure-containing polymers such as hydrogenated polystyrene, hydrogenated polyvinylcyclohexene and polyvinylcyclohexane.
(A) Method of Holding the Interiors of the Cylinder and Mold at a Low Oxygen Concentration State:
As specific methods for holding the interiors of the cylinder and mold at a low oxygen concentration state upon the molding, may be mentioned (1) a method in which the feed of a molten resin to a molding machine is conducted in an atmosphere of a gas containing oxygen only at a low concentration, and (2) a method in which the interior of an injection unit is held at a state of reduced pressure when a molten resin is fed to the injection unit to conduct injection molding, and the molten resin is injected into a mold to produce a molding.
(1) Method of Conducting the Feed to the Molding Machine in the Atmosphere of the Gas Containing Oxygen Only at a Low Concentration:
The method of conducting the feed to the molding machine in the gas atmosphere containing oxygen only at a low concentration is a method in which the feed of a resin material comprising the hydrogenated product of the aromatic vinyl polymer to the molding machine upon production of a molding by means of a heat melting type molding machine is conducted in an atmosphere of a gas containing oxygen only at a low concentration. As a result, lowering of molecular weight by oxidation, decomposition or the like, coloring of moldings, occurrence of silver streaks, and defective phenomena such as separation on the surfaces of moldings by adhesion of the hydrogenated product of the aromatic vinyl polymer to the mold are markedly improved.
The gas containing oxygen only at a low concentration is a gas inert to the hydrogenated product of the aromatic vinyl polymer and containing oxygen in;an amount of generally at most 2% by volume, preferably at most 1% by volume, more preferably at most 0.1% by volume, particularly preferably at most 0.05% by volume. Examples thereof include helium, neon, nitrogen, argon, xenon, crypton and carbon dioxide.
The inert gas used in the present invention desirably has a boiling point of xe2x88x92100xc2x0 C. of lower. When an inert gas having a boiling point exceeding xe2x88x92100xc2x0 C. is used, the inert gas is dissolved in the hydrogenated product of the aromatic vinyl polymer, and the dissolved gas vaporizes upon production of moldings, whereby the hydrogenated product of the aromatic vinyl polymer may foam in some cases, resulting in a molding having silver streaks or bubbles. Therefore, helium, neon, nitrogen, argon and xenon are particularly preferred.
The amount of the gas containing oxygen only at a low concentration used is preferably at least 30 liters, more preferably at least 60 liters, particularly preferably at least 120 liters per kilogram of the resin material fed to the molding machine, and the gas containing oxygen only at a low concentration is fed at this flow rate to create the gas atmosphere containing oxygen only at a low concentration.
In the present invention, the fact that the feed of the resin material is conducted in the gas atmosphere containing oxygen only at a low concentration means that air is replaced by the gas containing oxygen only at a low concentration for the purpose of preventing the hydrogenated polymer fed to the heating cylinder of the molding machine from melting under heat accompanied by air, thereby lessening the amount of air as much as possible or doing away with air. Namely, the feed of the resin material to the molding machine in the present invention is referred to the feed of the resin material to the heating cylinder of the heat melting type molding machine.
Examples of a method for creating the gas atmosphere containing oxygen only at a low concentration in order to replace the air accompanying the resin material by the gas containing oxygen only at a low concentration include a method in which a gas containing oxygen only at a low concentration is sent into a feed hopper for the resin material attached to a molding machine to make the interior of a cylinder a gas atmosphere containing oxygen only at a low concentration, a method in which a gas containing oxygen only at a low concentration is introduced into a heating cylinder of a molding machine at an optional position of the cylinder before a resin material is melted under heat to make the interior of the cylinder or the interiors of the cylinder and the above-described hopper a gas atmosphere containing oxygen only at a low concentration, and a method in which a resin material the air in which has been separately replaced by a gas containing oxygen only at a low concentration is fed to a cylinder.
No particular limitation is imposed on the heat melting type molding machine used in the methods for conducting molding at the low oxygen state, and examples thereof include injection molding machines and extruders.
(2) Method in Which the Interior of an Injection Unit is Held at a State of Reduced Pressure when a Molten Resin is Fed to the Injection Unit to Conduct Injection Molding, and the Molten Resin is Injected into a Mold to Produce a Molding:
The details of the method in which the interior of an injection unit is held at a state of reduced pressure when the resin material comprising the hydrogenated product of the aromatic vinyl polymer is fed to the injection unit to injection-mold it, and the molten resin is injected into a mold to produce a molding will hereinafter be described.
In the case of this method, gas is first discharged through a vent hole provided in a rear part of a cylinder of the injection unit, a feed hopper part for the resin material, or the like, thereby holding the interior of the injection molding machine (cylinder) at a state of reduced pressure.
The pressure within the cylinder is reduced to generally 15 Torr or lower, preferably 8 Torr or lower, more preferably 1 Torr or lower, particularly preferably 0.5 Torr or lower. The resin material is melted and injected under such reduced pressure, whereby for example, generation of a gas component from resin pellets, lowering of molecular weight by decomposition due to insufficient drying of the pellets, and occurrence of defective appearance of moldings, such as coloring of the moldings, occurrence of silver streaks, and separation on the surfaces of the moldings by adhesion of the resin material to the mold can be prevented. Further, it is preferable that air within the injection unit be discharged to purge the interiors of the hopper and cylinder with the gas containing oxygen only at a low concentration, and the injection unit be then vacuumed.
By the purging with the gas containing oxygen only at a low concentration as described above, the optical properties of the resulting molding, such as transparency, are more improved. The conditions for the injection molding conducted in the state of reduced pressure as described above may also be applied to the molding of, other polymers than the hydrogenated polymers according to the present invention.
(B) Method of Removing Dissolved Oxygen in the Molding Material Before the Molding:
Oxidation, decomposition and the like of a molten resin material can also be prevented by lowering the concentration of dissolved oxygen in a molding material (resin material) using, as a pretreatment in the above-described molding, a method of subjecting the resin material to a heat treatment, a treatment under reduced pressure, a replacing treatment under an inert gas atmosphere, or a combination of these treatments, and the same effect as the treatment upon the molding can be achieved.
An example of the method for lowering the concentration of dissolved oxygen in the resin material include a method in which the resin material is subjected to a heat treatment for 0.1 to 100 hours in a temperature range not lower than (Tgxe2x88x9260)xc2x0 C., but not higher than (Tgxe2x88x925)xc2x0 C., wherein Tg is a glass transition temperature of the hydrogenated product of the aromatic vinyl polymer, and then melt-molded. The heat treatment means that the resin is placed under an atmosphere within the above-described temperature range, and is not necessarily aimed at removal of water in the resin material.
The amount of dissolved oxygen is reduced by holding the resin material within the above temperature range. However, it is preferable that the resin material be treated under an atmosphere of low oxygen concentration at the same time. The atmosphere of low oxygen concentration means a gas atmosphere of an oxygen concentration as :low as generally at most 5% by volume, preferably at most 3% by volume, more preferably at most 1% by volume, or a state of reduced pressure of generally 15 Torr or lower, preferably 8 Torr or lower, more preferably 1 Torr or lower. Either method may be used.
Examples of the gas containing oxygen only at a low concentration include helium, neon, nitrogen, argon, xenon, crypton and carbon dioxide. An atmosphere of air diluted with any of the above-described inert gases in such a manner that the oxygen concentration is within the above range may be additionally exemplified.
No particular limitation is imposed on a dryer used in the heat treatment, and an ordinary hot-air circulating tray type dryer, hopper dryer, tray type vacuum dryer or agitated vacuum dryer used in drying of resin pellets may be used.
The resin pellets after the heat treatment are desirably used immediately in melt molding without passing away time. The time from the drying under heat to the molding is generally within 12 hours, preferably within 6 hours, more preferably within 3 hours, particularly preferably within 1 hour. In addition, the resin pellets are desirably held under an atmosphere of low oxygen concentration all the while.
In addition to the heat treatment, it is effective to adopt a method of keeping the resin pellets under an atmosphere of low oxygen concentration before the heat treatment is conducted. More specifically, the resin pellets are kept under a gas atmosphere of an oxygen concentration as low as generally at most 5% by volume, preferably at most 3% by volume, more preferably at most 1% by volume, in a state of reduced pressure of generally 15 Torr or lower, preferably 8 Torr or lower, more preferably 1 Torr or lower, or in a combined state thereof, for example, under an atmosphere of air diluted with the gas containing oxygen only at a low concentration and reduced pressure. The keeping time under such an atmosphere of low oxygen concentration is at least 1 hour, preferably at least 2 hours. Incidentally, the time required to create the atmosphere of low oxygen concentration may be a long time without any problem. For example, a bag or container little in oxygen transmission rate is used as a package upon packaging pellets after production of the pellets, the pellets are charged into the package under an atmosphere of low oxygen concentration, stored for a long period of time while keeping the interior of the package under the atmosphere of low oxygen concentration and then dried as they are. This process is also embraced in the present invention.
The above-described methods (A) and (B) may be effectively used in molding of the conventionally known hydrogenated products of aromatic vinyl polymers, and alicyclic structure-containing polymers, to say nothing of the molding of the specific hydrogenated products of aromatic vinyl polymers in the present invention because lowering of molecular weight by oxidation, decomposition or the like of the molding material, coloring of moldings, occurrence of silver streaks, and defective phenomena such as separation on the surfaces of moldings by adhesion of the hydrogenated product of the aromatic vinyl polymer to the mold can be prevented. The effects are marked upon the molding of substrates for information recording media in particular.
More specifically, (A) the molding method in which molding is conducted under the atmosphere of low oxygen concentration, or (B) the molding method in which the resin material is subjected to the heat treatment and/or the treatment under reduced pressure and then molded is used upon the molding of the resin material, whereby moldings small in birefringence, high in transmittance and little in surface defects by observation through an AFM, preferably substrates for information recording media are provided.
 less than Recording Film Layer greater than 
In the present invention, a recording film layer is provided on the substrate for information recording media, whereby the substrate can be used as an information recording medium. The recording film layer is an reflective aluminum film layer provided on the surface of the substrate or a layer provided in such a manner that the light reflectance may be irreversibly or reversibly and locally changed. The thickness thereof is several hundreds to several thousand angstroms, or at most 10,000 angstroms at the thickest.
In music CD, CD-ROM and the like, information itself is carved in a stamper part of a mold upon the injection molding, and minute grooves corresponding thereto are formed in the substrate. Therefore, a reflective film layer such as aluminum or gold is formed on a surface including the grooves by sputtering or the like, whereby the recording film layer is formed by the grooves and the reflective film layer.
In writ once CD-R, rewritable magneto-optical disk (MO) and the like, a recording film layer, which changes light reflectance or transmittance irreversibly or reversibly, a reflective film layer, which reflects light, and a thin, inorganic or organic protective film layer, which protects these layers and corrects optical strain, are formed. These layers are formed either singly or as a multi-layer structure in combination by a sputtering method, vapor phase growth method, chemical coating method and/or the like, thereby forming an information recording layer. In the use application to, for example, a magneto-optical disk, an information recording layer obtained by laminating a reflective layer composed of aluminum, gold or an alloy thereof; and a thin protective film layer composed of SiN, SiC or the like on a magneto-optical recording medium (for example, a recording medium of Tbxe2x80x94Fexe2x80x94Coxe2x80x94, Ptxe2x80x94Tbxe2x80x94Fexe2x80x94Co or the like) is used. In the case of a phase change type disk, an information recording layer obtained by laminating the same reflective film layer and thin protective film layer as described above on Texe2x80x94Gexe2x80x94Sb, Inxe2x80x94Sbxe2x80x94Te, Texe2x80x94Gexe2x80x94Cr, Texe2x80x94Gexe2x80x94Zn or an alloy thereof is used.
The thickness and forming process of these information recording layers vary according to the kinds of substrates for the respective information recording media, and the recording layers are formed according to the standard by a publicly known method.
 less than Coating Layer greater than 
When an information recording medium such as an, optical disk, making use of the substrate for information recording media according to the present invention, is used, a coating layer for protecting the above-described information recording layer from water and the like is generally formed before use.
(1) Coating Material:
A coating material used in forming the coating layer may be either a silicone coating material or an organic coating material. The silicone coating material is a partially hydrogenated product of a silane compound. Examples of the organic coating material include heat-curing coating materials such as melamine, alkyd, urethane and acrylic paints, and ultraviolet-curing coating materials composed mainly of a polyfunctional acrylic monomer or the like ultraviolet-cured. The ultraviolet-curing coating materials are preferred in that they can be cured under conditions that the hydrogenated products of the aromatic vinyl polymers are hard to be heat-deformed, and a coating layer having sufficient hardness and weather resistance can be provided.
{circle around (1)} Ultraviolet-curing Coating material:
The ultraviolet-curing coating materials of the present invention comprises a reactive monomer and/or a reactive oligomer, a photopolymerization initiator and other additives and is diluted with no or an solvent.
In the present invention, those having acrylate group(s) among photopolymerizable monomers are referred to as monofunctional monomers, bifunctional monomers, trifunctional monomers or the like according to the number of acrylate groups. In the present invention, the acrylate group also includes a methacrylate group, an ethacrylate group and the like in addition of the acrylate group in a narrow sense.
Examples of the monofunctional acrylate monomers include n-butyl acrylate, isoamyl acrylate, 2-hydroxy-ethyl methacrylate, 2-hydroxypropyl methacrylate, 2-ethyl-hexyl methacrylate, phenoxyethyl acrylate and phenoxy-propyl acrylate. Among these, those having only the acrylate group in a narrow sense without having a methacrylate group or the like are preferred so as not to inhibit a curing reaction with radical oxygen. Further, those having a side chain having about 4 to 6 carbon atoms are preferred in order to reduce cure shrinkage of a coating film to be formed.
It is also preferred that a long-chain aliphatic monofunctional acrylate monomer or alicyclic monofunctional acrylate monomer be used in order to improve the adhesion of the resulting coating material to hydrogenated product resins of aromatic vinyl polymers. As long-chain aliphatic monofunctional acrylate monomers, are preferred those having an aliphatic moiety having 5 to 18 carbon atoms, preferably. 8 to 16 carbon atoms. If the number of carbon atoms is too small, the adhesion of the resulting coating material becomes poor. If the number of carbon atoms is too great on the other hand, crosslinking is hard to occur, and the strength of the resulting coating layer is deteriorated. Specific examples of the long-chain aliphatic monofunctional acrylate monomers include lauryl acrylate, stearyl acrylate, octyl acrylate, isooctyl acrylate, decyl acrylate and isodecyl acrylate. Specific examples of the alicyclic monofunctional acrylate monomers include tricyclo[5.2.1.02,6]decanyl acrylate, a hydrogenated product thereof, isobornyl acrylate and cyclohexyl acrylate.
Examples of the bi- or trifunctional acrylate monomers include esterified products of polyols such as ethylene glycol, diethylene glycol, tripropylene glycol, butylene glycol, neopentyl glycol, hexanediol, trimethylolpropane, tetramethylolpropane, pentaerythritol and dipentaerythritol with 2 or 3 acrylic acids, and bisphenol F type epoxyacrylates. It is preferred that alicyclic bifunctional acrylates such as those described below monomer be used in order to improve the adhesion of the resulting coating material to hydrogenated product resins of aromatic vinyl polymers. Specific examples of the alicyclic bifunctional acrylate monomers include tricyclo[5.2.1.02,6]decanyl diacrylate, a hydrogenated product thereof, isobornyl diacrylate and cyclohexyl diacrylate.
Examples of tetrafunctional or still higher polyfunctional acrylate monomers include esterified products of polyols such as tetramethylolpropane, pentaerythritol and dipentaerythritol with a 4 or more, preferably 4 to 8 acrylic acids. Generally available tetra to hexafunctional acrylate monomers are particularly preferred.
As the reactive oligomers, may be mentioned polyester acrylates having an acryloyl group at their terminals, epoxyacrylates or polyurethane acrylates having an epoxy group in their molecular chains, and an acryloyl group at their terminals, unsaturated polyesters having a double bond in their molecular chains, an other oligomers having an epoxy group or vinyl ether group.
As examples of the photopolymerization initiator, may be mentioned acetophenones such as 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone and chlorinated acetophenone; benzophenones; benzoins such as benzyl, methyl o-benzoylbenzoate and benzoin alkyl ethers; azo compounds such as xcex1,xcex1xe2x80x2-azobisisobutyronitrile, 2,2xe2x80x2-azobispropane and hydrazone; organic peroxides such as benzoyl peroxide and di-tert-butyl peroxide; diphenyl disulfides such as diphenyl disulfide, dibenzyl disulfide and dibenzoyl disulfides.
With respect to mixing proportions of these components, the proportion of the monofunctional acrylate monomer is 15 to 65% by weight, preferably 25 to 60% by weight, more preferably 30 to 55% by weight based on the total weight of the acrylate monomer(s) and the photopolymerization initiator, the proportion of the bi-or trifunctional acrylate monomer is 5 to 50% by weight, preferably 6 to 40% by weight, more preferably 8 to 30% by weight, the proportion of the tetrafunctional or still higher polyfunctional acrylate monomer is 10 to 60% by weight, preferably 12 to 50% by weight, more preferably 15 to 45% by weight, and the proportion of the reactive oligomer is 0 to 60% by weight, preferably 10 to 50% by weight, more preferably 20 to 40% by weight. If the amount of the reactive oligomer is too great, cure shrinkage of a coating film to be formed becomes great, and the adhesion thereof is deteriorated. If the amount is too small, the viscosity of the resulting coating material, and so in some cases, an uniform film may be hard to be formed, or it may take a long time to cure the coating film.
The proportion of the photopolymerization initiator is 1 to 10% by weight, preferably 2 to 6% by weight. If the amount of the tetrafunctional or still higher polyfunctional acrylate monomer is too great, cure shrinkage of a coating film to be formed increases. If the amount is too small, the hardness of the coating film cured is lowered, and curing speed is slowed. If the amount of the monofunctional acrylate monomer is too small, the viscosity of the resulting coating material becomes high, and workability thereof is deteriorated. If the amount of the monofunctional acrylate monomer is too great, cure shrinkage of a coating film to be formed is reduced, and moreover the amount of the bi- or trifunctional acrylate monomer is lessened to deteriorate the flexibility of the cured layer, which forms the cause of occurrence of cracks. The amount of the bi- or trifunctional acrylate monomer is preferably greater in order to improve the adhesion of the resulting coating material.
The ultraviolet-curing coating material according to the present invention preferably comprises at least one monomer selected from the long-chain aliphatic monofunctional acrylate monomer, alicyclic monofunctional acrylate monomer and alicyclic bifunctional acrylate monomer in an amount of at least 40% by weight, more preferably at least 45% by weight, particularly preferably at least 50% by weight. The adhesion of the resulting ultraviolet-curing coating material to hydrogenated product resins of aromatic vinyl polymers is improved as the content of said at least one monomer selected from the long-chain aliphatic monofunctional acrylate monomer, alicyclic monofunctional acrylate monomer and alicyclic bifunctional acrylate monomer increases.
Proper additives may be added to the ultraviolet-curing coating material within limits not impeding the adhesion and hardness of the resulting cured layer. For example, a fluorine-containing nonionic surfactant is added, whereby the wetting of the substrate, and surface smoothness of the substrate after curing the coating layer can be improved. Besides, a proper thermoplastic resin is added, whereby the viscosity of the resulting coating material can be adjusted, and the adhesion thereof can also be improved. Examples of the thermoplastic resin capable of improving the adhesion include hydrogenated products of aromatic vinyl polymers, and resins similar in structure thereto, for example, ring-opening polymers of norbornene monomers, and petroleum resins such as dicyclopentadiene-based, diene-based, aliphatic and water-white resins or hydrogenated products thereof. {circle around (2)} Antistatic Agent:
When the ultraviolet-curing coating material is used as a protective coating material in particular, an antistatic agent is preferably added in order to prevent the electrostatic charge of the resulting cured layer. No particular limitation is imposed on the antistatic agent, and any commonly used antistatic agent may be used. However, a nonionic antistatic agent is preferred for the acrylate monomers. The nonionic antistatic agent is excellent in compatibility with the acrylate monomers, and a uniform ultraviolet-curing composition can be provided. Therefore, the resulting composition is uniform in adhesion and antistatic effect.
When the prevention of electrostatic charge is required of the cured layer (coating layer), the surface electric resistance of the cured layer is controlled to at most 5xc3x971013 xcexa9, preferably at most 2xc3x971013 xcexa9, more preferably at most 1013 xcexa9. In order to do so, it is only necessary to add the antistatic agent in an amount of 1 to 7% by weight, preferably 1.5 to 5% by weight. Even when the antistatic agent is added to and used for the ultraviolet-curing coating material in an amount necessary to sufficiently lower the surface electric resistance, a cured layer having adhesion not interfering with moldings formed of the hydrogenated product of the aromatic vinyl polymer from the viewpoint of practical use can be formed. If the adhesion becomes insufficient, it is preferable that a primer composition be used to form a primer layer as described below.
The above-described coating material may be used as it is. However, it may also be provided as an ultraviolet-curing coating material by dissolving the coating material in a solvent led by an aromatic hydrocarbon solvent such as toluene, xylene or chlorobenzene; an alicyclic hydrocarbon solvent such as cyclohexane or methylcyclohexane; a ketone solvent such as methyl isobutyl ketone, methyl ethyl ketone or acetone; or an ether solvent such as n-butyl ether or diethyl ether; or an ester solvent, cellosolve solvent, chlorine-containing solvent or the like at a concentration at least 80% by weight according to necessity of operability, and the like.
(2) Primer and Formation of Primer Layer:
In the present invention, the surface of a molding such as an optical disk is coated with the specific ultraviolet-curing coating material, which is then irradiated with ultraviolet rays to be cured, thereby forming a protective coating layer. In order to make adhesion between the resin material comprising the hydrogenated product of the aromatic vinyl polymer and the protective coating layer more firm, a primer may be applied prior to the coating of the ultraviolet-curing coating material. As the primer, is preferred a halogenated hydrocarbon polymer. Examples of such a halogenated hydrocarbon polymer include those obtained by halogenating a hydrocarbon polymer obtained by polymerizing or copolymerizing a hydrocarbon monomer such as ethylene, propylene, butadiene, isoprene or styrene, and those obtained by polymerizing or copolymerizing a halogen-containing monomer such as vinyl chloride, vinylidene chloride or chloroprene. Among these, those obtained by chlorinating the hydrocarbon polymers are preferred, with chlorinated polypropylene being particularly preferred.
The molecular weight of the halogenated hydrocarbon polymer is generally 5,000 to 200,000, preferably 10,600 to 150,000, more preferably 20,000 to 100,000. If the molecular weight is too low, the strength of the resulting primer layer is lowered. If the molecular weight is too high, the viscosity of the primer becomes too high, and so workability of the coating is deteriorated. The halogen content in the halogenated hydrocarbon polymer is generally 15 to 55% by weight, preferably 20 to 45% by weight, more preferably 25 to 35% by weight. When the halogen content is too low, adhesion between the protective coating layer and the surface of the molding is also deteriorated.
A photopolymerizable monomer, photopolymerizable oligomer or the like, which will be described subsequently, may be added as a reactive diluent to the primer. In particular, when a monofunctional acrylate monomer is added in a proportion of 2 to 20% by weight, adhesion between the protective coating layer and the primer layer and between the primer layer and the surface of the resin molding is improved, and so the protective coating layer is hard to be separated from the molding. It is hence preferable to add such a reactive diluent. The primer is preferably dissolved in a solvent to use it as a primer solution. No particular limitation is imposed on the solvent so far as it is a poor solvent for the hydrogenated product of the aromatic vinyl polymer. For example, toluene is a good solvent for the hydrogenated product of the aromatic vinyl polymer. However, when toluene is diluted to at most 70% by weight with methyl isobutyl ketone, corrosion of the molding formed of the hydrogenated product of the aromatic vinyl polymer by such a solvent is prevented to a small extent even when the solvent is applied to the molding. Therefore, such a diluted solvent may be used as a solvent for the primer.
A monofunctional acrylate such as n-butyl methacrylate or isoamyl methacrylate is also a poor solvent for the hydrogenated product of the aromatic vinyl polymer and a reactive diluent having an effect as a photopolymerizable monomer added to the primer as described above. Therefore, such a monofunctional acrylate is also preferred. The solid concentration of the primer solution is generally 1 to 30% by weight, preferably 1.5 to 20% by weight, more preferably 2 to 10% by weight. The primer layer is formed by applying the primer solution to the surface of a molding formed of the hydrogenated product of the aromatic vinyl polymer and fully removing a volatile component in the primer solution. However, when only such a reactive diluent as described above is used as a solvent for the primer, the removal process of the volatile component is unnecessary.
No particular limitation is imposed on a coating method of the primer solution on a coating surface. For example, spraying, dipping, spin coating, roll coating or the like may be adopted. No particular limitation is also imposed on the removal method of the volatile component in the primer solution. The volatilizing temperature and time required to substantially remove the solvent in the primer solution vary according to the kind of the solvent used, the coating weight of the primer solution and the shape of a coating surface of the molding. However, it is only necessary to determine the conditions thereof in such a manner that the temperature is at most about 100xc2x0 C. so as not to cause heat deformation of the molding formed of the hydrogenated product of the aromatic vinyl polymer, and the solvent can be fully removed. Specifically, it is proper that the coated molding is left to stand at about 60 to 100xc2x0 C. for about 3 to 60 minutes. It is preferable that the coated molding be cooled at room temperature for about 10 seconds to 10 minutes after the removal of the volatile component at a high temperature to cool it to a temperature almost near to room temperature.
No particular limitation is imposed on the coating weight of the primer solution. However, it is preferably such that the thickness of the coating film is about 1 to 10 xcexcm, particularly about 2 to 5 xcexcm. When the removal of the volatile component is necessary after the application of the primer solution, the coating weight is preferably controlled to give the above-described coating thickness after fully removing the volatile component. If the coating weight of the primer solution is too little, the effect of the primer solution is lowered. If the coating weight is too great, it is difficult to remove the volatile component, or a hard coating layer is easy to separate from the molding.
(3) Formation of Coating Layer:
In the present invention, the primer layer is formed on the surface of the molding formed of the hydrogenated product of the aromatic vinyl polymer as needed, and the ultraviolet-curing coating material is coated thereon,and then irradiated with ultraviolet rays to cure it, thereby forming a coating layer. The molding formed of the hydrogenated product of the aromatic vinyl polymer may be either a molding formed of a resin material itself comprising the hydrogenated product of the aromatic vinyl polymer or a combined product thereof with another material or molding. The coating layer is formed on the surface of the resin substrate and the recording film layer, or the whole surface thereof or, in particular, a portion of the surface, of which wear resistance and resistance to marring are required.
No particular limitation is imposed on a coating method of the coating material. For example, spraying, dipping, spin coating, roll coating or the like may be used. When the solvent is used, the coated substrate is fully dried after the coating, so as not to substantially contain the solvent. No particular limitation is imposed on the drying method.
The thickness of the ultraviolet-curing coating material is preferably about 2 to 300 xcexcm in coating, and about 10 to 400 xcexcm in adhesion. When the solvent is used, the coating layer is controlled so as to give this thickness after drying. If the thickness is too thin, any cured layer having high strength cannot be provided, and so a sufficient effect for improving surface hardness and sufficient adhesion cannot be achieved. If the thickness is too thick, it takes a long time to drying the coating layer and conduct a curing reaction, and so productivity is deteriorated. In addition, when the hardness is low due to insufficient curing, the cured layer is lacking in flexibility and may be cracked in some cases.
A coated surface is required to be sufficiently dried as needed. When the coating material is cured as it contains the solvent in plenty, the coating layer tends to crack, and the cause that a high-hardness coating film cannot be provided is formed. The drying temperature and time required to substantially remove the solvent vary according to the kind of the solvent used, the coating weight of the coating material and the shape of a coating surface of the molding. However, it is only necessary to determine the conditions thereof in such a manner that the temperature is generally at most about 120xc2x0 C. so as not to cause heat deformation of the base material, and sufficient drying can be conducted. Specifically, it is proper that the coating film is dried at about 60 to 120xc2x0 C. for about 3 to 60 minutes. It is preferable that the coating film be cooled at room temperature for about 10 seconds to 10 minutes after the drying at a high temperature to cool it to a temperature almost near to room temperature. Incidentally, when no solvent is used, the drying is unnecessary.
Thereafter, the coating film is irradiated with ultraviolet rays from a light source that effectively emits ultraviolet rays, such as a high pressure mercury lamp, whereby curing occurs in a short period of time to form a cured layer having a high hardness. The irradiation dose of the ultraviolet rays varies according to the reactivity of the photopolymerizable monomer(s) and photopolymerization initiator. However, the coating film can be generally cured in a period of time as short as about 5 to 10 seconds in the case of a high pressure mercury lamp of 80 W/cm.
These coating layers may also be not only used for the substrates for information recording media, which are formed of the specific hydrogenated product of the aromatic vinyl polymer according to the present invention, but also provided on substrates for information recording media obtained by molding the conventionally known hydrogenated product of aromatic vinyl polymers, thereby still more improving the reliability of the resulting information recording media.
Further, the above-described coating materials are excellent in such effects that surface slip is good when they are applied to moldings, the antistatic effect is excellent, and printing can be conducted thereon. Therefore, they are useful as protective coating materials, hard coating materials and the like for general moldings such as other optical parts making use of the conventionally known hydrogenated products of aromatic vinyl polymers, or other vinyl cyclic hydrocarbon resins.
Such a method is adopted, thereby providing substrates for information recording media having an excellent coating layer compared with the conventional coating layers, namely,
(1) a substrate for information recording media, composed of a resin material comprising the hydrogenated product of the aromatic vinyl polymer, and having a protective coating layer in which adhesion strength by a cross-cut peel test is at least 90%, and surface hardness (pencil hardness) is at least 2H,
(2) the substrate for information recording media set forth in (1), wherein the protective coating layer is formed by coating the surface of the substrate with an ultraviolet-curing coating material comprising a reactive monomer and/or a reactive oligomer, and a photopolymerization initiator and irradiating the coated surface with ultraviolet rays, and
(3) the substrate for information recording media set forth in (1) or (2), wherein the ultraviolet-curing coating material comprises at least one monomer selected from a long-chain aliphatic monofunctional acrylate monomer, an alicyclic monofunctional acrylate monomer and an alicyclic bifunctional acrylate monomer in an amount of at least 40% by weight.
 less than Surface Treatment greater than 
In the present invention, the surface of the substrate may be subjected to various surface treatments such as plasma treatment, corona discharge treatment, treatment with an active gas, solvent etching treatment, microsandblasting treatment and chemical etching treatment in order to mainly improve the adhesion of the recording film layer and coating layer to the substrate.
 less than Other Processes and the Like greater than 
In, for example, a digital video disk or laser disk, 2 disks formed in a half thickness may be used to laminate the disks on each other in such a manner that a recording film layer is located inside. A label or the like may also be further printed on the coating material by a screen process printing or the like. The respective processes recited in the present invention must be executed in order. However, other processes than these processes may also be added.
 less than Information Recording Medium greater than 
An information recording medium is produced by such processes as described above. Information recording media according to the present invention include optically readable information recording media and the like. Specific examples thereof include media incapable of rewriting, such as music CD, CD-ROM and laser disks, which make good use of changes in reflected light by minute irregularities, and media capable of writing once or rewriting, such as CD-R, WORM (writ once optical disk), MD (rewritable optical disk; magneto-optical disk), MD (minidisk) and DVD (digital video disk), which make good use of changes in reflectance by functional coloring matter or phase change. With respect to an optical information recording medium disk having a conductive film layer formed of aluminum, gold, iron or the like, or a compound containing such a metal atom as, for example, a reflecting film layer, when a corona discharge treatment is intended after forming the conductive film layer, there has been a risk of discharge, and so such a treatment has been impossible. However, the production process according to the present invention is adopted, whereby scorch or burning by discharge is prevented, and so adhesive force between the respective layers can be improved. Therefore, such a production process is preferred.
 less than Optical Part greater than 
The resin materials according to the present invention have sufficiently small birefringence and excellent mechanical strength and are excellent in moisture resistance, and molding and processing ability, and are hence suitable for use as not only the above-described substrates for information recording media, but also all optical parts of which these properties are required.
Examples of optical parts for which the molding materials according to the present invention can be used include the conventionally known optical parts which can be molded from plastics, such as optical lenses, prisms, mirrors, medical inspection cells, light guide plates and optical films. More specifically, the optical parts are used in a wide variety of application fields, such as whole beam transmission type lenses such as image pickup system lenses in a camera, image pickup system lenses in a video camera, microscope lenses, endoscope lenses, telescope lenses, binocular lenses, spectacle lenses and magnifying lenses; pickup lenses for optical disks such as CD, CD-ROM, WORM (writ once optical disk), MO (rewritable optical disk; magneto-optical disk) and MD (minidisk); lenses in a laser scanning system, such as fxcex8 lens and sensor lens for a laser beam printer; and prisms lens in a finder system of a camera. Examples of the optical parts according to the present invention also include optical lenses such as infrared sensor lenses, auto-focus lenses and band-pass filter lenses, with the above-described absorbent, dye and/or pigment incorporated therein; optical mirrors; prisms; light guide plates for liquid crystal display devices and the like; various kinds of inspection cells, such as medical blood inspection cells; and optical films such as deflecting films, phase difference films and light diffusion films.
The moldings according to the present invention are suitable for use as various kinds of medical transparent moldings of which a repeated steam sterilization treatment, which is conducted under severer high-temperature and high-humidity conditions, is required. Specific examples thereof include containers for liquid, powdery or solid chemicals such as container for liquid chemicals for injection, ampoules, prefilled syringes, transfusion bags, containers for solid chemicals, containers for eye drops and container for drops; sample containers such as sampling test tubes for blood inspection, bleeding test tubes and specimen containers; medical devices such as injectors; sterilizing containers for sterilizing medical devices; and medical optical parts such as plastic lenses for drug inspection. The resin materials according to the present invention are also suitable for use as insulating materials, hardware for treatment of semiconductors, etc.
Among the resin materials according to the present invention, those comprising a hydrogenated polymer, wherein the content of foreign matter having a particle diameter of at least 0.5 xcexcm in the hydrogenated polymer is extremely low, have small birefringence and excellent mechanical strength and are excellent in moisture resistance, and molding and processing ability, and are hence suitable for use in various kinds of optical parts. Among the optical parts, use application to optical lenses are preferred. In particular, the hydrogenated polymers with an antioxidant blended with a solution of such a polymer are particularly suitable for use as optical lenses.
The optical lenses according to the present invention can be improved in optical properties, chemical resistance, wear resistance, moisture permeability, etc. by providing a hard coating layer formed of an inorganic compound, organic silicone compound such as a silane coupling agent, acrylic monomer, vinyl monomer, melamine resin, epoxy resin, fluororesin, silicone resin, or the like on the surfaces thereof by a method such as heat, curing, ultraviolet curing, vacuum deposition, sputtering or ion plating.
The resin materials comprising a hydrogenated polymer, wherein the content of foreign matter having a particle diameter of at least 0.5 xcexcm in the hydrogenated polymer is extremely low, are excellent in properties such as transparency, heat resistance, water resistance and resistance to acids and alkalis and moreover have a feature that the content of foreign matter is low, and are hence also suitable for use as moldings, such as carriers such as IC carriers, wafer carriers, information recording medium carriers, carrier tapes and wafer shippers; lids thereof; materials for ultrapure water systems such as containers for ultrapure water and piping materials for ultrapure water; hardware for treatment of semiconductors, such as joints for piping, containers for liquid chemicals and cleaning tanks. More specifically, when the moldings according to the present invention are used in various hardware used in production processes of integrated circuits, such as storage.shipment, surface treatment, etching treatment with a liquid chemical and ultrasonic cleaning treatment of silicon wafers, failure in products by fine foreign matter can be prevented even when they are used in production of extremely integrated semiconductors such as ultra LSI and ULSI, since occurrence of finely particulate foreign matter is extremely little.